comstock



n. F. COMSTOCK. PRODUCTION OF COMPLE MENT'AL IMAGES.

-APPLICATION FILED MAR 16, I920.

Reissued Nov. 16, 1920.

To all whom. it may concern:

UNITED f s'ra'r"as DANIEL I". GOMSTOGK, OF CAMBRIDGE MASSACHUSETTS,ASSIGNQR T0 'KALM'US,

PATENT OFFICE.

GOMS'IOCK & WESCOTT, INCORPORATED, OF BOSTON, MASSACHUSETTS, A 003-IOBATION OF MASSACHUSETTS.

Be it known that I, DANIEL F'. CoMsTooK, a citizen of the United States,and resident of Cambridge, in the county of Middlesex and State ofMassachusetts, have invented new and useful Improvements in theProduction of Complemental Images, of which the following is aspecification.

This invention relates to the production of undistorted multiple images,and more particularly the invention relates to a compound lens system ofa. multiplex motionpicture camera for simultaneously forming,

accurately in the same plane, two or more substantially perfectcomplemental images ofa. scene, the complemental images being formedfrom the same point of view.

In color motion-picture projection it has heretofore' been thecommercial practice to. project successively through color-screens,

film pictures taken successively through color-screens. The resultsobtained by this method have been open to twoserious objections; first,the displacements in successive pictures of moving objects cause thoseparts of the moving objects, which [do not coincide in the successivepictures, to appear in the colors of the several color screens ratherthan in the natural colors which would result from the blending orfusionof the several colors; secondly, the eye is fatigued by thealternate bombardment of light of different colors. The first difficultycauses what are called fringes and is especially bad when rapidly movingobjects are photographed. The second dif-- ficulty causes a feeling ofeye strain which is distinctly objectionable.

To overcome this, it is desirable to project simultaneously throughdifferent colorscreens two or .more photographs, taken throughcolor-screens, of the same scene from accurately the same point of Viewat the same time. This involves the problem of obtaining on. a film orfilms two or more i photographs from accurately the same point of view,of the same 'sceneat the same time.

. In the production of complemental pictures for color motion-pictureprojection it vis not only essential tofree each individual picture fromaberrations owing to the -high degree of magnification employed in the;

projection of the picture upon a screen, but

it is of equally great importance to correct rnonuo'rron or coMPLEMEnrALIMAGES.

Specification of Reissued Letters Patent. Reissued NO 1-6, 1 920Original No. 1,280,667,- dated October 8, 19 18, Serial No. 121,931,filed Septem for reissue filed. March 16, 1920. Serial No. 366,383.

each picture in the same manner and to the same degree; otherwise, whenthe comple-' Theproblem of obtaining twoorf nore;

ber 25, 1916. Application.

color lmages of the same scenexfrom 'th'e 1 same point of view at thesame time through the same lens system for the motion pic ture film, iscomplicated by numerous prac tical difiiculties. In general, it involvesdividlng the light-into two or more similar but separate beams, andreflecting the divide'd' beams upon the filinin the film-gate or otherfilm positioning means, and so re fleeting the light throughout. thesystem, that clear images appear in the plane of the film. The moreobvious ways of doing this are, for various reasons, unsuitable for themotion picture field; I

For example, an ordinary photographic objective may constitute theentire lens system, and some form of polished metallic grid, withreflectors of similar type, may be used to divide and to reflectthebeams so that clear images fall in the plane of the film. Such a systemis markedly unsatisfactory for two reasons. In the first place,

the surface of the metal grid and reflectors easily becomes oxidized,tarnished, mechanically injured, or covered with a' deposit of dust orother'foreign. substance which cannot readily be removed \withoutmechanically injuring the surface; and even when such mirrors are notvisibly damaged by;

any of the above means, they may still have their coeflicients ofreflection markedly changed through the lapse of evens'hort spaces oftime. The deterioration of metal- 11c reflectmg surfaces may seem atrivial in practice to use such reflectors successfully for camera work.a v

Ifthe'metallic surface is protected by a plate of glass, it is clearthat the front surface of the lass will also reflect light, and

difficulty, but it has been found. impossible influence is. found to belessthan might be imagined, as they are all more or 'less' p0 rous orpermeable and consequently do not protect the surface adequately. Suchsubstances are likewise soft andeasily abraded.

' Again-, if such metallic mirrors are used, it

will in general be found that the mounting of them and the meansnecessary for adjustment will require "a considerable increase in thelength of path above the length which would appear necessary on a simplegeometric diagram.

The second objection to the use of such a system is based upon the factthat it is highlyadvisable, for reasons of; perspective,

size of picture, depth of focus, etc., that whatever lens system is usedin motion picture work should in general have a relatively shortequivalent focal length; and this means, of course, that if an ordinaryphotographic objective constitutes the entire lens system,'it must be ata relatively short distance measured along the light rays,

fromthe film. It will be found in general that short focallengths areprohibited when such a metallic system is used, because of-the spacerequired in getting the light diw'ded and reflected tov form separateimreflecting surfaces,

of the surfaces where the light enters and leaves the prisms reflectslight, and, ac-

cording to the particular structure used, the

- stray light falling on the image due to such to provide a method ofand apparatus reflections, will be more or less pronounced. Thedifficulty of mounting and adjusting also applies to this case.

The'object of this lnvention therefore? is or simultaneously producing,accurately of the same size and preferably in the same plane, aplurality of complemental imagesof an object field, taken simultaneouslyfrom the same point of view; and for producingthe complemen'tal imagesin such manner that they are substantially identical and sub stantiallyfree from astigmatism, spherical and chromatic aberrations, whereby theimages, when projected in superposed relation upon a screen may be,accurately registered throughout.

In the face of the above difficulties the present invention followsmarkedly radical any other uncorrected component, it renders imperfectany perfect image transmitted through it. Through shaping the surfacesWhere the light entersand leaves the composite component, it is possibleto reduce the aberrations in such a transmitted image, but in generalthey will not in this way be completely removable.

Inorder to obtain real images and have them reasonably perfect, aspecially designed positive lens component must be combined with thecomposite component in thepath of the light from the object to thisfilm. ,This positive component must be so" proportioned that theresultant lens as a whole is a relatively perfect positive lens with itsrear nodal point at a proper distance from the film. Indeed, it can beshown that, in the particularform of the device illustrated, the rearnodal point is nearer the image plane than-the forward surface of thecomposite element, i. 6., that the rear nodal point of the system iswithin the composite element. Thereforeysince as far as the-image isconcerned, the resultant lens system is'virtually situated at its rearnodal point, the equivalent focal length of the system is markedlyshorter than the shortest focal length which can be used if thereflecting, dividing region is not'filled with the optically densemedium.

- My composite lens system s.tisfactorily meets the difficulties aboveenumerated. Such metal surfaces as are necessary are coated on a surfaceof glass, which surface, since it is simply the boundary of the densemedium itself, involves no ghosts and serves as an adequate protection.for the .metal film itself. Moreover, the possibility of having the rearnodal point of the entire lens system within the composite elementitself removes largely or entirely the lengthof-path difliculty.

In the accompanying drawings,-

Figure 1 is one embodiment ofmy invention showing one combination ofpositive and composite components of the lens system;

Fig. 2 is another embodiment of the invention showing a different typeof positive lens in combination with the composite component; and

v Fig. 3 is another modification of the combination comprising a furthertype of posi. tive component.

lines. 'It abandons polished metal mirrors, A In each of the figures thepositive comand abandons the ordinary photographic ponent ofthe lenssystemjs designated as ob ect1ve as constituting its lens system. It PCand the composite component is desig involves'filling a large part ofthe dividing .nated as CC. -The positive component is and reflectingsystem with a transparent medium as optically dense as practicable.objective but is designed in such' manner Such a light dividing,reflecting and trans asto adapt it to form in combination with mittingmedium comprises a generalized the composite component, a spherically,

somewhat similar to the ordinary camera lens component and ishereinafter referred chromatically. and astigmatically correctedto asthe composite component. But like 'lens system. 11.1 each embodiment thelight" to cut off stray reflections and thereby avoid from the objectfield enters the lens system from the left, is formed into an imagebearing beam the size of which is controlled plan I, preferably inspaced relationship with respect to each other.

The composite component CC comprisesa separate lenses-or groups oflenses placed in I the paths of the divided beams respectively.

In accordance with the principal object of the invention, the lenssystemcomprising the two elements of the character described is very carefullycorrected for the follow ing aberrations, namely, primary curvature offield, secondary curvature of field, spherical aberration, axialchromatic aberration, oblique chromatic abplurality of glass prisms P PP and P erration, coma, etc. In color motion-piccemented together asshown, the risms P and P conslsting of 45 rhombs, 2 consisting of a 45triangular prism, and P consisting of a planearallel block. Between;

theprisms P and 2 is arranged a lightdivlding means which preferablycomprises a grid designed according to the invention such as illustratedin the drawings, is adapted respectively-to transmit andto refleetone-half 'of'the image-bearing beam. The faces R R and R of-the prisms Pand P are arranged to function, respectively, as total reflectingsurfaces for the reflected and transmitted portions of the image-bearingbeam. Color screens which;

for example, may comprise a red screen RS- and a green screen GS, areplaced in the paths of the respective image-bearing beams between therear faces of the prisms andthe image plane I for transmitting onlythe'components of the light which have the desired dominant hues. Dams Dof black balsam are preferably placed at the proper positions theformation of ghosts on the film.

As will be hereinafter more fully explained, an important feature 'ofthe par-' ticular arrangement of the composite component hereinillustrated. consists in, making the paths of the complementalimage-bearing beams therein of substantially the same length, thelengthof the paths being measured along the ray passing through thecenter of the positive component, along the axis 'of the positivecomponent, and along the central rays of the separate beams which passthrough the center of the respective complemental images; that is,making the distances along the dot and dash lines from,

thegrid G, where the main image-bearing beam is divided, to the rearfeature faces of the prisms P and P substantially equal.

.This feature is of particular importance in systems of the type hereinillustrated in which the positive comppnent vcomprises a lens. group orgroups placed in the path of the main beam inasmuch as in systems ofthis typethe positive com onent can not affect the divided beams dierently to correct for difi'er'encesin the respective divided beams asit can in systems of the type in which the positive component comprises'trated in Fig. 1.

gether.

ture photography for which the lens system is particularly adapted,it isdesirable that these aberrations be either wholly elimiorconcavesurfaces in the paths of the I image-bearing beams, i or by making thepaths of the complemental image-bearing beams of slightly differentlengths; or, the correction of the aberrations of the entire system maybe made wholly in the positive element, that is, the positive elementmay .be designed in such a way that when used in combination with thecomposite element, the

aberrations of the entire system will be corre:.ted. with out curvingthe faces of :..the prisms and without making the paths through theprisms of unequal length.

One system of the type in which the positive component isspeciallydesl'gned to correct the aberrations of the entire lenssysteni, comprises the positive component PC and the composite component:CC, fillu's- The positive component is of the general type having foursingle lenses arranged in two groups, the two groups being separated bythe diaphragm. The two elements of one group are separated by an airspace while, the two elements of the other group are cemented to- Thepairof facing surfaces have a negative power while the pair ofcementedesurfaces have a collective effect} This results in the,positive component having a comparatively small number of lenses, there-.by reducing reflections, affording a relatively large aperture andaffording a relatively large area of anastigmatic flatness of O the fourlenses of the positive component PC the lenses L and L are positive andthe lenses L and L, are negative. The group 11,, L is separated from thegroup L L by a diaphragm The lenses L,, L, are separated by an air spacebounded upon systems in which the dense medium.

by facing surfaces which have a dispersive effect and the lenses L L arejoined by a cemented surface having a collective effect. The data forthe lens s stem comprising the components PC and C are as follows:

Positive component.

nD=1.612o na' rez ss CF=0.01045 mensions are in inches and the variouschar-' acters have the following significance; 1' 1' etc., refer 'to theradii of'curvaturefof the various lens surfaces; t 2%,, etc, representthe thicknesses of the lenses; d d etc., represent the distances betweenthe adjacent surfaces of the lenses and between the lenses anddiaphragms; Z and Z represent the lengths of the paths of the componentbeams in the prisms; n n represent the refractive indices of the-glassesused for D- light and G'-light, -respectively; and is the dispersivevalues Of thB lenses for the range of light between the C and F lines ofthe spectrum. Although data are given for only one focal length inconnection with each embodiment of the invention, it is to be understoodthat data for systems for other focal lengths may be derived by makingproportional changes for; all dimensions involved. Furthermore, the dataare based comprising the composite component has an index of refractionfor D-light of 1.573 and a dispersive value of .00995 for C-F light,although the data are substantially accurate for a considerable range ofoptical media.

In the embodiment of the invention show .111 Fig. 2 the positivecomponent PC is distinctly different from the positive component PC,illustrated in ig. 1. This component comprises two groups of. lenses,the forward group of which comprises a positive lens'L and a negativelens L and the rearward group of which comprises a negative lens L,, apositive lens L5, and a positive lens L Each of the positive lenses Land L is composed of highly refractive baryt-crown glass and thenegative lnses L and L,-are composed of glass having a low refractivepower, the two groups of lenses being separated by an air space of thatthe surface of the negative lens of the positive meniscus form. Therespective surfaces of each of the two negative. lenses L and Lpreferably have different degrees of curvature, and the lenses arepreferably so arranged with respect to the diaphragm front group whichhas the greater degree of curvature faces the diaphragm, and so that thesurface of the negative lens of the rear group having the lesser degreeof curvature faces the diaphragm. It is also preferable that the forwardgroup of lenses should have i a focal length greater than the focallength of the rearegroup, but that the focal length of the forward groupshould not exceed approximately twice the focal len th of the reargroup. The positive lens 9 prefer-- ably has a focal lengthsubstantiallythree times the'focal len th of the entire positive component PC. helens may be. plano convex; or indeed, the surface facing the compositecomponent CC may even, be weakly positive, but preferably the lens is ofpositive meniscus form having a surface. of negative curvature facingthe composite component. The lens L is made of glass having a lowdispersive power, for example, a glass with a refractive index'for Dlight of 1.5116 and whose mean dispersive power is 1/60.3. 95

Fige2 also illustrates means whereby the separate divided beams may eachbe further corrected individually. This,comprises making the faces ofthe prisms in the paths of the separate beams concave and convex,respectively, the face of the prism P 'which is in the. path of the beamintended to form the red image being made convex, while the face of theprism P, which is in the path of-the beam intended to form the greenimage is madeconcave.

These curvatures may or may not be employed and, when they are employed,they,

.serve as means for further correcting the oblique. chromatic,aberration of the lens 1 system. In the particular embodiment of L theinvention, illustratedin Fig. 2, the curvature of the surfaces of therespective prisms should differ by approximately 1.25 diopters,

and while each surface is illustrated as have ing a curvature of halfthis amount, the surface of prism P having a positive curvature 1 of0.625jdiopters and the surface of prism P having a negative curvature of0.625 diopters, it is to be understood that thedifference of curvatureof 1.25 diopters might be divided in any other desired manner; andindeed, the entire curvature might be applied to' one prism leavingtheface of the other prism flat. When the faces of the prism are curved forthe purpose of further correcting the oblique chromatic aberration, theprisms must be fixed in position with re-' spect to the image plane,whereas this condition is not essential when the faces of the lenses LL,,, L

' follows:

prisms are not curved, as in Fig. 1. In either event, as well as in theembodiment illustrated in Fig. 3, the positive component need not bemaintained in any particular fixed relationship with respect to thecomposite component of the system.

The data for the specific embodiment of the invention illustrated inFig. 2 are as Positive component.

Composite component.

,nG'= 1.5225 C-F=0.00839- Aperture 'ratio=1:3.5

In the third embodiment of the invention illustrated in Fig. thepositive lens component PC" com rises a group of four arranged withrespect to each other and with respect to the diaphragm d 1n a mannersimilar to that shown in'Fig. 1. these lenses differing, how-. 7 ever,in, specific dimensions and spacing distances as shown by the t'ableofdata be-.

low. In addition to these fourlenses the posi- 1' I tive component PC"comprlses a forward protection for the lens L the latter being rou oflenses L L and L The lenses i 12 form a cemented doublet having a focallengthwhich is practically infinlte and the lens comprises a fla't plateof glass of uniform thickness which serves. merely as a of suchcharacter as to require a protective covering. The lenses L L comprisingthe doublet are preferably composed of glasses whose indices differ byat least 001?. A characteristic of "this particular emb od1- ment of theinvention is that for D-light the focal lengths of the two elements ofthe doublet are substantially equal and the internal nodal points lieclose together, thus making a substantially non-magnifying lens element.V

In order to correct the axial chromatic aberration of the system toasomewhat higher degree thanis otherwise atta nable, the length of pathsof the divided image'- bearing beams may be made slightly difierent.Thus, as illustrated in Fig. 3, the path of. the reflected beams oflight passing through prisms-P and P, and being projected through agreen color screen to form the green image is .004: of an inch longerthan the path of the beam of li ht which is transmitted through the ridpassing through prisms P and 3 and thence through a red color screen toform the red .70 image.

The specific data of the lens system shown in Fig. 3 are as follows: 1

Positive component.

length=2.67. 'Aperture ratio==1:5.5

Composite component. z',',=-2.704 I .Iclaimr K 1. A lens system forforming a plurality of-complemental images of the same objectfield,comprising a positive lens component adapted to form animage-bearing beam of a light containing substantial aberrations, meansfor dividing the image-bearing beam of light into a plurality ofseparate but similar image-bearing beams, and optically dense retractingmedium filling the light-dividing region and forming a continuouspath-in the dense medium for each separate beam throughout thelight-dividing region, the optically dense retracting medium forming acomposite component which, in combination .With the positive component,comprises a spherically and chromatically corrected lens system.

2. A. lens system for forming a plurality of complemental images of thesame object field from the same point of view, compris ing a positivelens component adapted to form an image-bearing beam of light containingsubstantial aberrations, means for di- .vidingthe image-bearing beam oflight into a plurality of separatebut similar imagebearing beams,reflectors-in the. paths of the separate beams to project the severalimages upon the same image plane, and an optically dense'refractingmedium filling'the light-dividing and reflecting region and forming acontinuous path for each separate beam throughout the light-dividing andreflecting region, the optically dense refracting me- 'dium formingacomposite lens component whicl1,'in combination with the positivecomponent comprises a spherically and chromatically corrected lenssystem.

3. A lens system for forming a plurality of complemental images of anobject field from a single point of view comprising a positive lenscomponent adapted to form an imagebearing beam of light, a grid fordividing the image-bearing beam of light into a plurality of separatebut similar image-bearing beams, anda composite component comprisingjuxtaposed glass prisms filling the maj or portion of the space betweenthe positive component and the image plane, the-glass prisms whollysurrounding said grid and having reflecting surfaces in the pathsof theseparate beams for projecting the several images upon the same imageplane, the posiponent comprising an optically dense rebination with thecomposite component, a

fracting medium filling the major portion of the space between thepositive component and the image plane, the optically dense re: fractingmedium wholly surrounding said grid and having reflecting surfaces inthe paths of the separate beams for projecting the several images uponthe same image plane, the pos1t1ve lens component being constructed insuch manner as to form, in comspherically, chromatically andastigmatically corrected lens system, the rear nodal "point of thesystem lying within the composite component whereby the back focallength of the system is less than the thickness of the compositecomponent. 7

5. A lens system for forming-a plurality of complemental images of anobject field from a single pointof view comprising a positive lenscomponent adapted to form an image-bearing beam of light containingsubstantial aberrations, a reflecting-transmitting grid for dividing theimage-bearing beam of light into a plurality of separate but similarimage-bearing beams, a composite component comprising juxtaposed glassprisms filling themajor portion of the space between the positivecomponent and the image plane, the glass prisms wholly surrounding saidgrid and having reflecting surfaces in the paths of the divided beamsfor projecting the several images upon thesame image plane, the positivelens component being constructed in such manneras to form, incombination with the composite component, a spherically, chromaticallyand astigmatically corrected lens system, the back faces of the prismsbeing curved difi'erent degrees in the respective paths of the complemental image-bearing beams for correct,

ing oblique chromatic aberration, and color screens positioned in therespective paths of the complemental image-bearing beams.

6. A lens system for forming a plurality of complemental images of anobject field from a'single point of view comprising a positive lenscomponent adapted to form animage bearingbeam of light, means to dividethe image-bearing beam of light into a plurality of image-bearing beams,and a composite component comprising an optically dense retractingmedium filling the major portion of the space between the positivecomponent and the image plane and forming a continuous path ofsubstantially equal length for the plurality of image-bearing beams, thepositive lens component being constructed to form, in combination withthe composite component, an a'stigmatically, spherically andchromatically corrected lens system adapted to form the complementalimages in such manner that they are each of the same size and similarlycorrected.

7. A lens system for forming a plurality of complemental images of anobject field from a single point of view comprising a positive lenscomponent adapted to form an image-bearing beam of light, the positivelens component comprising four lenses separated by a diaphragm intotwogroups of two lenses each, one of said groups having a pair of facingsurfaces of negative power and the other of said groups having acemented surface of positive power, and a composite component comprisingan optically dense refracting-medium including means for dividing saidimage-bearing beam into a plurality of image-bearing beams adapted toform the complemental images, the positiye lens component beingcorrected to form, v

in combination with the composite component, a spherically,chromatically. and astig-.

matically corrected lens system. i

8. A lens system for forming a plurality of complemental'images of anobject field from asingle point of view comprising a positive lenscomponent for forming an image-bearing beam oflight, and a compositecomponent, the latter comprising an 4 optically dense refracting mediumincluding means for dividing said image-bearing beam into a plurality ofimage-bearing beams adapted to form the complemental images, thepositive lens component being undercorrected in such manner and to suchextent as to torm,.in combination with the composite component, aspherically, chromatically and astigmatieally corrected lens system.

9. A lens system for forming a plurality of complemental images of anobject field from a single point of view, comprising a positive lenscomponent for forming an image-bearing beam of light, means for dividingthe image-bearing beam into a plurality of similar image-bearing beams,and a composite component for transmitting the plurality of similarimage-bearing beams from the beam-dividing means to the respective imageregions, the composite element comprising an optically densetransmitting medium filling the major portion of the paths of theplurality of similar imageb;earing beams, the positive element beingconstructed and arranged alone to form an image-bearing beam of lightcontaining substantial aberrations but being constructed and arranged incombination with the composite component to form a plurality ofimage-bearing beams of light containing substantially no aberrations.

10. The method of simultaneously pro ducing a plurality of complementalimages of an object field from a single point of view comprising,forming an image-bearing beam of light containing substantialaberrations, dividing the image-bearing beam into a plurality of similarimage-bearing beams, pass ing the similar image -bearing beams throughan optically dense medium, reflecting the similar image-bearing beamswithin the dense medium in such manner that they form complementalimages substantially in a single plane, and introducing into theimage-bearing beams by the passage through the dense medium aberrationsadapted to counteract the aberrations in the original image-bearingbeam, whereby the complemental images are spherically, chromatically andastigmatically corrected.

11. The method of simultaneously producing a 'plurality'of spherically,chromatically and astigmatically corrected complemental images of anobject field from a single point of view comprising, forming animage-bearing beam of light by means introducing aberrations ,thereinto,dividing the image-bearing beam into a plurality of similarimage-bearing beams, passing the similar image-bearing beams throughanoptically dense medium to thereby increase the distance between theimage-forming means and the image region and .to thereby introduce intothe image-bearing beams aberrations of such nature and of such'extent asto counteract the aberrations introduced into the original beams.

12. The method of producing a plurality of complemental images of anobject field comprising, producing an imagebearing beam of light havingsubstantial aberrations and dividing the image-bearing beam into aplurality of similar image-bearing beams in such manner as to introduceaberrations opposed to the former aberrations, thereby forming aplurality of spherically, chromatically and astigmatically correctedcomplemental images.

13. A lens system for forming a plurality of complemental images of anobject field from a single point of view comprising composite andpositive components arranged in voptical alinement for dividing thelight into a plurality of similar beams and focusing the divided beamsin the same plane, the composite components being formed of an opticallydense transmitting medium and the positive components being constructedand arranged alone to produce substantial aberrations but in combinationwith the composite components to form a plurality of images containingsubstantially no aberrations.

l4. Alens system for forming a plurality of complemental images of anobject field from a single point of view comprising composite andpositive components arranged in optical alinement for dividing the lightinto a plurality of similar beamsand focusing the divided beams in thesame plane, the composite components being formed of an optically denserefracting medium and the positive components being constructed to form,in combination with the composite components, an astigmatically,spherically and chromatically corrected lens system adapted to form thecomplemental images of the same size and similarly corrected.

15. A lens system for forming a plurality of complemental images of anobject field from a single point of view comprising composite andpositive components arranged 1n optical alinementfor dividing the lightinto a plurality of similar beams and focusing the divided beams in thesame plane, the composite components being formed of an optically denseretracting medium and the positive components being constructed andarranged to introduce aberrations substantially equal and opposite tothe aberrations introduced by said refracting medium, whereby thecomplemental images are substantially free; from aberrations.

Signed by me at Boston, -Massachusetts this 5th day of March, 1920.

' DANIEL F. COMSTOCK.

image bearing

